Saturday, February 03, 2007

r180 rear end conversion

okay. so I got myself a christmas present (and a hell of a conversion to do on christmas eve).

4 corners worth of brembos with hubs and full R180 rear diff conversion parts. (thank you fineline imports!)

key things to consider:


to do the Front brembo convesion you need to:

1. have wheels to clear the big bad mofo's. USDM Sti bbs is popular, so is Sti JDM/UK 17's.

2. Clear your rear struts with the big tires and offsets that the brake clearance requires - on a GC8 with JIC coilovers (more tire clearance than a stock strut style), this ment a 4mm spacer and camber adjuster bolts to make camber ~-.75 deg in the rear. otherwise you rub tire against coilover/shock and that is bad news.

3. if above criteria is met, then all thats left to do is to pony up the cash and grab a front set. Install, Bleed (both inside and outside bleed nipples).
- note, the bleed nipples are 11mm. WEIRD.

REAR brembo conversion $$$$$$$ X 2!~!

stupid, but i had to do it :P

theres 4 routes to take here.

#1 $$$$$$$ X 1.0
#2 $$$$$$$ X 2.0
#3 $$$$$$$ X 2.25
#4 $$$$$$$ X 1.50

#1 $$$$$$$ X 1.5 :
- keeping R160 rear hubs is the premise
Buy rear brembo calipers. Buy rear rotors to fit the brembo brakes:
A: buy Godspeed's adapter kit ~$600: you get 2 caliper bracket adapter brackets (CNC machined id assume) and a Rotor insert that you put inside the stock rear Brembo rotor to make the E-brake inner diameter go from 190mm->170mm (unless you dont want an e-brake.

Another option commonly seen is a rear rotor that has a 170mm e-brake but Big diameter rotor to fit the caliper.

all solutions to doing this and keeping the R160 rear hubs is about $600 or so.

r180 hub backing plate vs R160 caliper. NOT compatible, but with an adapter you can put a R180 brake on a R160 hub. use logic.... visualize!

$ budget solution for option #1 $$$$$$$ X 1.5 : approx $1100 or so.

#2 $$$$$$$ X 2.0

Buy rear brembo calipers + rotors + big R180 hubs + R180 axels +R180 diff.

how to do:

1. remove rear hubs, brakes, axels, diff.
2. replace With R180 diff, R180 axels, R180 hubs, r180 brembo calipers / rotors

-If you are using GDB rear diff (most will be bc gc8 r180 is RARE) you will need to swap rear diff studs as they are differnt lengths:


vice-grypts or double nut works the matJiK

- R180 GDB axels are longer than R180 GC8 to my understanding, but they work just proper (just drove home from the shop with my r180 rear end).

- putting axelstubs in diff and hub first before connecting makes life easier.
- R180 Diff has a differnt driveshaft than R160 (for 5mt). a GC8 5mt R180 driveshaft DOES exist. it is rare.
- R180 6mt driveshaft is obviously differnt (shorter - same length as automatic 4eat).


R180 rear diff ive only seen in 4.44 and 3.9. unless you have a 4.44 JDM or FXT box, or a 3.9 usdm ej22t 5mt, or a usdm wrx with a 1:1 centre diff conversion, this wont really work for you. no 4.11 that i know of, or 3.54 R180 rear diff.

** im not saying it dosnt exist, it would most likely be from a nissan or somthing. (they use R180's as well)

if you have a 5mt and want to use a R180 rear diff you have 3 options:

1. source an ultra rare R180 5mt driveshaft from JDM STi version 4/5/6 RA with r180 rear diff.
2. Drill out the R180 diff flange to 4 bolt smaller diameter pattern of the R160 driveshaft. the inner rounded bit is actually identical between R180 and R160 so it fits proper (after you drill out the holes - cobalt bit and patience is recommended - took a good 30 minutes to drill 4 holes).
3. Swap big diff flange of R180 diff to a R160 diff small flange - impact gun + vice or the like.

- i choose both 2 and 1. my #1 is in the mail :

after these snarfus are overcome, life is good.

bleed, etc, etc

- Keynotes - GDB R180 rear hub is widertrack. 4mm spacer is no longer required for 225/45/17 070 to clear my rear coilover.

- this assembly is HEAVY. adds an extra 40 lbs or so to the rear end. YUK.

- Brembos are overly sexxy. you may catch yourself looking at them all the time.

__________________________________________________ ___________

bonus round.

#3 $$$$$$$ X 2.25
#4 $$$$$$$ X 1.50


#3 $$$$$$$ X 2.25
- same as #2, bute with more cash required!!!

BALLER wabits and the like.

same swap, but with 114.3 conversion from jdm V9 sti or usdm 05/06.
-requires the 5X114.3 wheels instead of 5X100. so budget for some nasty ADVAN RG's or the like and the front hub conversion to match cool..

#4 $$$$$$$ X 1.50
- same as #1 $$$$$$$ X 1.0 but more labor required and slightly more cash:

Instead of rear brembos, fit OEM JDM Sti-RA 2 piston black "subaru" brakes with hub/axel/brake/R180 conversion. same rules apply as #2 ($$$$$$$ X 2.0), just less nasty on the budget (and harder to source).

this will mostly be done by the hardcore rally guys to fit 15" gravel wheels.
- if you want to do the brakes w/o the good stuff, then theres a good thread on the backing plate game, or you can swap in the R160 hubs from a 2006 usdm WRX.

Any questions or suggested appendages to the FAQ, please post or PM.

MOre pictures will be posted shortly!!




After a couple bloody knuckles: and 8 hours on christmas eve....

Notes on drilling for driveshaft adaptation

theres no worry on that one. i was paranoid- trust me, but i talked it over with a couple ME's and they gave me the thumbs up! so i went for it.

ill snap some shots when i get a chance. it dosnt have to be perfecly in line either, there are alot of multipattern drilled brake rotors and wheel spacers that are sold by big companies that dont hvae things spaced out perfectly. as long as the spacing is correct.

if you drill through the driveshaft, theres no way you'll do it wrong.

ill post a pic if i get a chance to (dont really want to pull my driveshaft covers today but will when i get my new driveshaft in..),

but just trust me on this one for now??

the driveshaft uses 4 tiny bolts - 6mt and 5mt driveshaft and diff is same size.

some logic (I dont feel like learning or doing the math- although my kindergarden teacher said i am fully capable of it):

[this info from my discussion with engineer from DANA axels/driveshafts]

- oem 2 piece driveshaft is balanced in the front, the rear, and the diff is balanced on its own.
- oem driveshaft has middle rubber doughnut thing. that guy will eat the harmonic variances if some
- even if oem driveshaft WAS out of balance, it is built oem to roughly 2X the tensile load and vibration capacity - on a motorsports part sure we use alot, but its still got a saftety windog
- from research, subaru guys do NOT brake driveshafts or driveshaft bolts / diff flanges / driveshaft flanges.

from various RWD conversions we see that:

#1 to break: rear diff gears
#2 stepper gears on centre diff
#3 - perhaps rear axels>? Kingpin guys where are you [id say that kingpin has the best example of high PS RWD subaru]

i'm sure its possible, but i have never heard of anyone breaking a subaru driveshaft or diff flange yet-

from the looks of it the tiny 4 12mm head bolts would shear before the flange would break.

ALSO- my key point in being willing to risk this:

centre of R160 and r180 driveshafts / diffs has the same innie/outie pair. it is a perfect fit OEM in that the parts meet up perfectly (anyone whos pulled a driveshaft on a subaru will know, if you havn't you are technically a noob like my title here!)

also, the driveshaft is balanced with little stick on weights. if for some weird reason you messed up the balance on the diff flange, it would be equivilent to perhaps one of those little weights falling off. no sweat, people loose wheel weights all the time and never realize it untill they get tires mounted and balanced.

Your standard variation in manufacturing is probably more than a 8mm deep 4mm wide hole could ever be :P

1 comment:

Terron said...


Thanks for all the great info.

On the topic of brakes; are the JDM 98 GC8 WRX front brake calipers the same as the 98 USDM RS brake calipers?